1. Field of Invention
The present invention relates to a virtual computer system, in particular, to a technique for dynamically reallocating a resource for a virtual computer corresponding to a load of the virtual computer.
2. Description of Related Art
In a virtual computer system, physical resources such as a CPU, a main memory, and an IO are logically partitioned and allocated to each virtual computer LPAR (Logical Partition) realized on the virtual computer system. Mechanisms which allocate physical resources to a virtual computer dynamically in a virtual computer system are disclosed in Japanese Laid-Open Patent Publications No. 6-103092 and No. 6-110715. In the virtual computer system disclosed in the above-mentioned publications, when allocation of physical resources of LPAR is to change, operation by an operator or time driven (to drive when a timer reaches a set time) issues a re-allocation demand to a program (hypervisor) for controlling a whole virtual computer system. The hypervisor dynamically changes the allocation of LPAR according to a resource allocation method configured before the operator issues the reallocation demand.
Moreover, the hypervisor also includes a monitoring function for collecting a system operation condition such as a CPU time of each LPAR. In these devices, operators need to decide allocation of physical resources, and after allocating resources automatically from the system operation condition, it is not possible to automatically re-allocate them. However, according to Japanese Laid-Open Patent Publication No. 9-26889, a device is suggested in which one LPAR inquiries a hypervisor about CPU time of another LPAR within the same virtual computer system, and when there is a difference between the actual CPU time and set allocated CPU time, the allocated CPU time is matched with the actual CPU time. However, the CPU time does not always representing a load condition of the computer system correctly. Moreover, it is difficult to improve a response property of the system by simply increasing the CPU time.